The invention relates to a process for determining a patient's circulatory fill status, particularly the global end-diastolic volume GEDV, intrathoracic blood volume ITBV, pulmonary blood volume PBV, extravascular lung water EVLW, and/or global cardiac function index CFI; with this process the intrathoracic thermo-volume ITTV and pulmonary thermo-volume PTV are determined by means of thermo-dilution. The term "circulatory fill status" as used herein encompasses the fill statu of any part of a patient's circulatory system.
In the critical-care diagnosis and treatment of extremely sick patients, cardiac output C. O. and circulatory fill volume are important characteristics.
A pulmonary catheter is currently in wide use; it can be used to measure cardiac output C. O. by the thermo-dilution process and, as parameters for circulatory filling, to measure central venous pressure CVP, right ventricular end-diastolic volume RVEDV, and pulmonary-capillary wedge pressure PCWP. In this connection see D. Payen "Physiological Determinants of Hemodynamic Parameters" from "Strategy in Bedside Hemodynamic Monitoring," published by J.-F. Dhainaut and D. Payen, Springer-Verlag, 1991, pp. 28-35.
Measuring the pressures CVP and PCWP against atmospheric pressure has the decisive disadvantage that it is not possible to derive the circulating volume from these values reliably. In addition, the values CVP and PCWP, which are often referred to as circulatory fill pressures, are not very sensitive to changes in volume. In this connection see U. J. Pfeiffer et. al. "Sensitivity of Central Venous Pressure, . . . " from F. R. Lewis and U. J. Pfeiffer "Practical Application of Fiberoptics in Critical Care Monitoring," Springer-Verlag, 1990, pp. 25-31.
Because this was realized, the measurement of the RVEDV value was introduced, but this value is indicative only of the fill volume of one of the four ventricles. Moreover, there is a considerable degree of variation in the determination of the RVEDV value. In this connection see J.-F. Dhainaut et al. "Validity and Clinical Applications of Fast Response Thermistor for Right Ventricular Ejection Fraction Monitoring," from J.-F. Dhainaut and D. Payen: "Strategy in Bedside Hemodynamic Monitoring," Springer-Verlag, 1991, pp. 59 ff.
A more specific process for measuring cardiac output C. O. and circulatory fill volume is the so-called thermo-dye technique. This technique is a combination of dye dilution DD and thermo-dilution TD and makes the intrathoracic blood volume ITBV available as a specific parameter for circulatory filling. The value encompasses the right-atrial end-diastolic volumes RAEDV and right-ventricular end-diastolic volume RVEDV, the blood volume of the lungs (pulmonary blood volume) PBV, and the end-diastolic volumes of the left atrium LAEDV and left ventricle LVEDV. This process has the further advantage that the extravascular water of the lung EVLW can also be determined. In this connection see U. J. Pfeiffer et al. "A Fiberoptics-Based System . . . " in U. J. Pfeiffer "Practical Application of Fiberoptics in Critical Care Monitoring," Springer-Verlag, 1990, pp. 115 ff.
The thermo-dye process has the disadvantage, however, that it requires the injection of a relatively expensive dye, in which connection, because of its sensitivity to light and heat, the injectable dye solution always has to be made up right before the injection, i.e., at least once a day. In addition, the dye may cause allergic or anaphylactic reactions.
The fiber-optic thermistor catheter used in this process is very expensive as a disposable item. Moreover, the corresponding measurement device is also relatively expensive due to the fact that a reflection photometer is used to measure the dye concentration.
Fiber-optic dye measurement may also be impaired by problems with optical measurement, e.g., due to deposits on the optical eye of the measurement catheter, dislocation of the measurement catheter, etc. Finally, because of the size of the fiber-optic thermistor catheter, thermodye dilution measurement can be done only in the femoral artery. The measurement catheter sizes that have been common to date make it completely impossible to take measurements on children or infants.